"There are over 150 different species of plants that are on the roof," the spokesman for the Chicago Department of the Environment said, gesturing at a carpet of plants near his feet. "They're basically things that don't need a lot of maintenance."

Merritt is 12 floors above the ground on Chicago City Hall's "green" roof, an example of environmental design that has drawn the interest of private and public sector building owners across the country, including the Asheville City Council in North Carolina.

The rolling mounds of shallow-rooted grasses and crab apple trees filter storm water and cool Chicago's landmark building, and could serve as a model for a cap on the ailing Civic Center in Asheville, N.C., some members of city council say.

On Oct. 24, council voted to earmark $1.5 million for a new roof for the center and to take alternative proposals for green designs. Structural reports have said the downtown center for arts, entertainment and conventions is sorely in need of a new top.

Important support for the green alternative could come from Councilman Jan Davis, a longtime proponent of renovating the center.

"If there is an economy in doing it, I am all for it," he said of a green roof design. A moderate, Davis might join environmentalist council members in voting for a green roof.

Proponents point to benefits that include lowering city temperatures, reducing stormwater runoff and improving air quality.

"It doesn't necessarily have to come back cheaper than the traditional roof because there are intrinsic values," chief green roof supporter Councilwoman Robin Cape said.

In Chicago, where heat-absorbing materials amplify hot summers, City Hall's green roof has temperatures up to 70 degrees lower than the adjacent Cook County building asphalt roof, environmental department staff said. That translates to lower city air conditioning bills, Merritt said.

"Also, the roof holds onto 80 percent of the rainwater," he said, "and lets it out over a longer period of time."

That, he said, means less strain on municipal sewerage systems and less pollution in streams and rivers.

Less tangible pluses include greening the city landscape and adding habitat for birds, butterflies and grasshoppers that hitched a ride on plants. Bees also live on the roof and their honey composition appears to show that they frequent flowers a mile away at the new Millennium Park, Merritt said.

The choice of Chicago's City Hall as the first green roof in the city was no accident, City Environmental Commissioner Sadhu Johnston said. Chicago has used the grassy pulpit and a grant program to spur 250 other such public and private projects, including roofs on a health food store and a Wal-Mart.

"If we can bring the temperature in the city down by just one degree, we could save $150 million on air conditioning," Johnston said.

Those pushing the idea in Asheville, N.C., say the city could reap similar environmental benefits. Doubters point to the high price tag attached to the new technology.

"There is what is nice. And there is what is necessary," Councilman Carl Mumpower said. "This is more nice than necessary."

Estimates for vegetating the 47,000-square-foot Civic Center roof range from $660,000 to nearly $1.2 million. A standard asphalt design would likely run $560,000 to $670,000, according to a cost study.

Cape and other proponents argue that the difference would be offset by immediate cost savings including a 25 percent reduction in air conditioning needs, not having to pay $1,000 in stormwater fees and tax credits for energy efficient design.

Architect Peter Alberice, whose firm Camille-Alberice Architects put a partial green roof on their downtown building, said long-term benefits include not having to replace the roof for 40 years -- possibly three times as long as a traditional roof.

"To me, it would be a complete waste of money to put a regular roof on that if they are going to keep the building," he said of the center.

Alberice does caution about potential pitfalls. Getting materials from just one supplier can help with warranty issues should something in the system fail, he said.

Also, the bottom membrane should be thoroughly tested for holes, since water leakage could lead to expensive repairs, said architect Alan Wingfield with Colbond Inc. The Netherlands-based Colbond has a plant in Enka, N.C., that makes parts for green roofs and has more than 20 years experience with the systems in Germany and elsewhere, Wingfield said.

Roof systems vary widely in scope, from grassy parks with trees to thin layers that do not stand much foot traffic. Older buildings, such as the center, are usually not engineered for the additional weight and take a lighter system.

That type of information and cost estimates will drive whether a green roof is a reality for the building in Asheville, N.C.

Should the main roof prove unworkable, another possibility is to focus on the 19,000 square-foot concourse roof, Davis said.

Either way, the councilman sees the possible image changing effect for a building disparaged as out-of-date and in need of repair. The spotlight would shine especially bright in the environmentally conscious western North Carolina town.

"This may be the thing that takes the stigma away from the building," Davis said.